Drafting head assembly

ABSTRACT

A drafting head for a drafting machine has two scaled straightedges directable at right angles to one another to define x and y coordinates, and carried by a member provided with an annular path of rotation. The member is constrained to the annular path for accurate angular adjustment of the straightedges, and the center line of this path passes through the vertex of the operating positions of the two straightedges. Each of the two straightedges in its operative position leaves clear drafting space in the vicinity of the operative station of the other straightedge, but means are provided to permit the drawing of lines to and through the above-mentioned vertex along the operating position line of each straightedge, and also to permit the drawing of lines radiating into each of four quadrants from a common center without moving the drafting head.

United States Patent Bullard, [II

FOREIGN PATENTS OR APPLICATIONS [111 3,766,651 1451 Oct. 23, 1973 Primary Examiner-Harry N. Haroian Attorney-Ronald J. St. Onge et al.

[57] ABSTRACT A drafting head for a drafting machine has two scaled straightedges directable at right angles to one another to define x and y coordinates, and carried by a member 'provided with an annular path of rotation. The

member is constrained to the annular path for accurate angular adjustment of the straightedges, and the centerline of this path passes through the "vertex of the operating positions of the two straightedges. Each of the two straightedges in its operative position leaves clear drafting space in the vicinity of the operative station of the other straightedge, but means are provided to permit the drawing of lines to and through the above-mentioned vertex along the operating position 882,661 9 1953 Germany....'. .i 33 79 R line f each straightedge, and also to permit e draw- 990,745 6/1951 France 33/79 R g of lines radiating into each of four quadrants from a common center without moving the drafting head.

6 Claims, 10 Drawing Figures 150a v I I480- l l I I46 /82 /50a [5041 I I83 SHEET 2 0F 6 PATENTEDUETZS I973 IIIIIIIIIIIIII'IIIIIII II PATENTED BET 231973 SHEET '4 BF 6 sun-:1 s ur e PATENTEUUET 23 1975 PATENTEDHCI 2 1913 sum 6 or e DRAFTING HEAD ASSEMBLY This is a continuation-in-part of my prior application Ser. No. 114,833, filed in my name on Feb. 12, 1971 and now abandoned.

BACKGROUND OF THE INVENTION The drafting machines used heretofore however have suffered from a number of shortcomings For one the mounting for the drafting head movement has generally lacked the rigidity necessary to produce the very high accuracy drawings presently required by'rnany industries. in my copending application Ser. No. 1 14,833 entitled Drafting Machine and filed Feb. 12, 1971 I'disclose a digital input drafting machine constructed for the production of highly accurate drawings, and in which the drafting head of the present invention may be used to advantage. It will be readily understood by reference to that copending application that the relatively flimsy drafting head mountings in prior art drafting heads are not tolerable in a modern,high accuracy drafting machine since the inaccuracies introduced thereby will all but cancel out the extreme accurac built into the actuating mechanism.

The typical prior art drafting head has also subjected draftsmen to inconvenience because of difficulties in accomplishing desired drafting operations at or near the intersection points of intersecting lines. Because of More specifically, the drafting head comprises an angularly adjustable carriage bearing a pair of straightedges which have effective operating positions at right angles to each other. The carriage is equipped with an annular part which is rotatable under the governance of precision guide means (for example, a strongly constructed annular track) having a desired orientation with respect .to the drafting surface. By this means, the drafting head is provided with the structural rigidity needed for the production of high accuracy drawings as required. by modern industry.

Another feature of the invention is that the center of rotation of the angularly adjustable portion of the drafting head (the center of rotation being a point lying on the common center line of the annular carriage part and its guide means) is aligned with the vertex of the projection lines of the two straightedges in their respective operative positions. The said vertex is accordingly the origin of the coordinate system defined by the operative positions of the two straightedges, and, in the preferred applications of the invention, the natural zero point of the scale marking of each straightedge coincides with this origin when that straight-edge is in its assigned operating position. Accordingly, the draftsman may draw measured'radial linesdirected from the origin at any angle merely by rotating the drafting head in place, and no change in the coordinate system represented by the two straightedges occurs. Accordingly, the draftsmans task is much simplified in respect to a basic, frequently reoccuring function. Moreover, the fact that each new position of the drafting head over the drafting surface defines a unique coordinate system which need not be disturbed to draw intersecting lines renders the drafting head of the invention ideally suited for combination with digital input drafting machines.

In the preferred form of the invention,'each of the two straightedges in its operativ position leaves a subthis, the entire drafting head may have to be moved about excessively to draw even a simple geometric shape such as a rectangle.

Accordingly, it is an object of the present invention to provide a drafting head whichis constructed to overcome the particular difficulty just referred to, but which further is simply yet ruggedly constructed, accurate and reliable.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

SUMMARY OF THE INVENTION The present invention relates to an improved drafting head for a drafting machine, and more particularly to a drafting head which exhibits the structural rigidity necessary to produce accurate drawings and whith enables a draftsman to draw basic figures with fewer motions by providing tool-guiding parts that are mounted for controlled and accurate manipulation about a strategically chosen center point which is itself readily movable over the drafting surface.

stantial gap between its origin-directed end and its natural origin orzero point (i.e., the vertex or point of intersection of the projections of the two straightedges.) This has value from a drafting standpoint in that it permits small scale drafting operations to be conducted without impediment in the vicinity of the origin, but, on the other hand, it precludes using the straightedges now under consideration for producing lines projected through the origin. In this preferred form of the invention, I therefore provide in the vicinity of the origina pair of concurrently movable supplementary straightedges which are controllably manipulatable between two operating positions. In one of these positions, the first supplementary straightedge provides a continuous extension of one of the primary straightedges to and through the origin, while still leaving free drafting space in the vicinity of the end of the other straightedge. In the other position, the second supplementary straightedge performs an identical service in reference to the second primary straightedge. As a result, the drawing of measured lines which intersect at a common origin of measurement is much simplified, and at the same time, the performance of small scale drafting additions in the vicinity of the origin is made possible with far fewer movements of the drafting head.

The drafting head is also provided with protractor means for determining the degree of angular rotation of the rotatable carriage portion and with means for locking or automatically detaining the carriage at selected angles of rotation, features which further enhance the ease of operation and the accuracy achievable by the draftsman.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a front perspective view of the drafting head assembly of the invention as used on one type of an automated drafting machine.

FIG. 2 is an enlarged partial top plan view of the drafting head assembly.

FIG. 3 is a further enlarged sectional view taken along line 3-3 of FIG. 2.

FIG. 4 is a partial top plan view, shown partly in section, taken along line 44 of FIG. 3.

FIG. 5 is a further enlarged partial sectional view taken along line 5-5 of FIG. 2.

FIG. 6 is a top plan view of a second embodiment of the invention.

FIG. 7 is an enlarged sectional view taken along line 7-7 of FIG. 6.

FIG. 8 is a partially broken away side elevation taken on line 88 of FIG. 6.

FIG. 9 is a bottom plan view of the construction of FIG. 6, certain parts being removed.

FIG. 10 is a plan view of an alternative application of certain aspects of the invention.

Similar reference characters refer to similar parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drafting head of the invention may be used with a variety of drafting machines. One kind of drafting machine with which it amy be used to particular advantage is a digital input type such as that described in my previously discussed copending application. As seen generally in FIG. 1, the drafting machine includes a drafting board 6 tiltably mounted on a base 8 in order to establish a desired inclination of the drafting surface 9. The drafting head, generally indicated at 10, rests on the drafting surface and is pivotally connected to a main carriage 12 supported on a main rail 13 for transverse movement relative to drafting board 6. The main rail is supported by top rail 13a and bottom rail 13b for longitudinal movement of the head 10.

Referring now to FIG. 2, drafting head 10 is 'connected to carriage 12 by means of a frame member 14. The size and configuration of frame member 14 is generally dictated by the structure of the carriage 12 to which it connects, and will vary for different applications. For the apparatus shown in FIG. 1, however, frame member 14 comprises a generally flat plate 16 having a pair of connector tabs 18a and 18b secured by screws 19 or the like and projecting from the rear edge 20 thereof. Tabs 18a and 18b respectively carry connector pins 22a and 22b which project laterally therefrom. Pins 22a and 22b are made to respectively drop into slots 24a and 24b (see FIG. 3) in carriage arms 26a and 26b to form a secure interconnection between carriage l2 and drafting head 10. This pin and slot interconnection also permits drafting head 10 to ride up and down to adjust for board irregularities or paper thickness, and to be pivoted up off drafting boards so that drafting paper sheets can be easily changed. Similarly,

the pin and slot interconnection facilitates removal of the drafting head for repairs or adjustments, and permits, if desired, the ready substitution of similar, moclular drafting heads of varied configuration.

In addition to connecting drafting head 10 to the main body of the drafting machine, frame member 14 also provides an annular track for guiding the angularly adjustable portions thereof-As shown in FIG. 2, track 30 is an imaginary path preferably defined between a series of roller guides, some of which are radially offset from the others to delineate the track width w. The number of roller guides used will normally depend upon the size of the drafting head, more rollers typically being used in larger structures. For the embodiment shown, however, three roller guides are sufficient; two of the roller guides 32 and 34 are respectively journalled to bosses 36 and 38 which project from the preferably arcuate forward edge 40 of frame member 14. The third roller guide 42 is preferably journalled to frame member 14 in the same manner (FIG. 3) at a point along track 30 approximately half-way between rollers 32 and 34. Roller guide 42 is however radially offset from guides 32 and 34 by an amount equal to the desired track width w. Roller guides 32, 34 and 42 are also preferably ball bearing mounted to minimize friction and prevent binding and may be journalled in eccentric mountings to permit fine adjustment of their position.

Although rolling members are preferred as track defining means, other means may be used. For example the rollers may be replaced by fixed, low friction members such as nylon bearings; alternatively, track 30 may be defined by spaced, continuous arcuate strips of low friction material secured to member 14, or it may be an annular channel machined into the surface of member 14.

Still referring to FIG. 2, the angularly adjustable portion of drafting head 10 comprises a pair of primary straightedges 44 and 46 projecting at right angles to each other to define x and y ordinates, and with their line of intersection forming a vertex 45 which coincides with the center of track 30. The term vertex is used herein to denote the point of intersection of the respective drawing edges x and y of straightedges 44 and 46 when they occupy the operative positions shown. The intersection is of course an imaginary point in the case of separated straightedges, although it would be a physical entity if the straightedges were connected. Vertex 45 in my drafting head is also the origin of the coordinate system defined by the straightedges. It should be noted, however, that in recognition of the fact that every pen or other such scribing device has a finite width, the actual location of drafting edge of each straightedge may be displaced a few mils from the ideal line projected through the vertex just mentioned this displacement being established as close as may be to one half the width of the scribing tool. For this reason, it is necessary to say that the projection of each straightedge passes substantially through the origin, and by this word to mean that the displacement, if any, is very slight.

straightedges 44 and 46 are preferably wholly separate devices formed typically from a transparent plastic material and scribed with suitable scale indicia 47 for drafting purposes. The straightedges may be removably attached to a separate support member 48 by screw knobs 50 or the like so that they can be readily replaced if damaged, or interchanged with straightedges having different scale indicia. The screw portion of each knob 50 preferably passes through a slotted hole 51 in support member 48 so that slight lateral adjustment of each straightedge is possible. Although the structures bearing the straightedges have been depicted as being rectangular in shape, it will be understood that they may take other convenient shapes. Further, in applications where the advantages resulting from interchangeability are not required, straightedges 44 and 46 and support member 48 may be either permanently secured together or formed integrally.

Support member 48 preferably comprises a pair of relatively broad flanges 48a and 48b directed at right angles to each other, and which'respectively serve to support (by means of removable screw knobs 50) straightedges 44 and 46, which are thus maintained in relatively orthogonal positions. Flanges 48a and 4812 are joined by an arcuate segment 52 which carries on its top surface an annular protractor rail 54 in the form of a raised, annular shoulder. The radial dimensions of rail 54 are equal to or just slightly less than the width w of track 30 so that rail 54 can fit and slide within track 30in rolling contact with rollers 32, 34 and 42 as shown in FIG. 4. Preferably, rail 54 is also provided with upper and lower edge flanges 54a and 54b (FIG. 3) which together provide a guideway 540 for roller guides 32, 34 and 42. Since roller guides 32, 34 and 42 are held in guideway 54c, the structure serves to hold frame membervl4 and support member 48 together whenever drafting head l0is pivoted off the drawing board or removed from carriage 12. A knob 55 may be provided on framemember 14 to facilitate such pivoting or removal. The structural combination of a protractor rail riding in a track defined by the special roller guides of the invention has been found to provide the structurally rigid and precision mounting which is needed for highly accurate drawing.

Thus it can be seen that in use, drafting head. 10 rests on drafting board 6 with the primary straightedges 44 and 46 in contact with the drafting surface 9 (FIG. 1) or more typically the surface of a sheet of drafting paper secured to the board.

In this position, straightedges 44 and 46 can be simultaneously manually rotated about the common center line C (FIG. 3) of both track 30 and rail 54 to any angular disposition desired by the draftsman. To enable the determination of the degree of angular rotation achieved, the upper surface of rail 54 is preferably provided with a protractor scale 56 marked in degrees as shown in FIG. 4. A vernier scale 58 denoting minutes of arc is' also preferably provided on a plate 60 either secured to or forming a part of frame member 14 (FIG. 2). Vernier scale 58 lies adjacent anedge 62 of plate 60 which is shaped to conform closely to and abut rail 54 so that vernier scale 58 and protractor scale 56 can be read together. In the position shown in FIG. 4, the zero markings in both scales are in register indicating that straightedges 44 and 46 are aligned with the edges of the drafting board in the manner illustrated in FIG. 1.

Means are also preferably provided for securing the adjustable portion of drafting head 10 at any selected angular orientation. A preferred device for this purpose is a friction brake 'which, as shown in FIGS. 2 and 4, comprises a friction block 63 formed or faced with a high-friction material. Block 63 is journalled at one end 64 to the underside of frame member 14 and extends tangentially to rail 54. The opposite end 66 of block 63 is connected by an eccentric rotatable cam 67 embedded therein (FIG. 4) to a pivot pin 70 secured to a small brake arm 68 mounted atop frame member 14 (FIG. 2). It can be seen from FIGS. 2 and 4 that by manually rotating brake arm 68 between the positions shown in dotted and solid lines, the side 72 of block 63 can be brought to frictionally bear against the adjacent side of rail 54. This serves to prevent the movement of rail 54 in track 30 and thus fixes the angular orientation of straightedges 44 and 46 at any desired position.

An additional mechanismmay also be provided to permit quick and accurate adjustment of the straightedges at predetermined angular increments without need for careful adjustment by the operator. For this purpose a detent lever 74 is mounted on a pivot 76 to frame member 14 as shown in FIGS. 2 and 5. A spring 78 extends between frame member 14 and detent lever 74 behind pivot 76 and thus biases lever 74 in a clockwise direction as seen in FIG. 5. The forward end 80 of lever 74 pivots through an opening 81 in frame member 14 (FIG. 5) and carries a counter-bored detent aperture 82 on its lower surface facing rail 54. Rail 54 in turn is provided with aplurality of detent pins 84 which project slightly abovethe upper surface thereof. Aper ture 82 is aligned to receive any desired pin 84 and thus lock the adjustable portion of drafting head 10 against movement. Detent pins 84 may be incrementally spaced as desired along the length of rail 54, a particularly useful spacing being at common degree increments, i.e., 10, 15, 20, 30, 45, etc., as shown in FIG. 4. Accordingly, a draftsman may readily release drafting head 10 for rotation by manually squeezing detent lever 74 against frame member 14 to the position shown in dotted lines in FIG. 5. The draftsman may then. grasp either straightedge 44 or 46 and manually rotate part 48 to move the desired member of incremental detent pins 84 on rail 54 past lever 74. A channel 85 (FIG. 2) is provided in the undersurface of frame member 14 to accommodate the movement thereunder of pins 84. At the desired position the draftsman merely releases lever 74 which then rotates clockwise (FIG. 5) under the bias of spring 78 until aperture '82 received and engages the appropriate pin 84 to lock the apparatus in position. The knobs 50 (FIG. 2) preferably provided for one or both straightedges 44 and 46 facitate manual rotation thereof by the draftsman. Stop pins 87a and 87b are also preferably provided at either end of rail 54 (FIG. 2). Pins 87a and 87b contact .the edges of bosses 36 and 38 to prevent the rotation from exceeding the extent of protractor scale 56. f .Referring again to FIG. 4, it can be seen that straightedges 44 and 46 are preferably separate devices which are unconnected at their vertex 45. Accordingly, an area of discontinuity or gap 86 exits between the most nearly adjacent (intersection-directed) ends 44a and 46a of the straightedges. This gap is important for purposes of the present invention, although without the additional provisions shortly to be described would limit the length of line the draftsman could draw with each straightedge without moving drafting head 10, and would also require movement of the drafting head in order to draw a complete right angle at vertex 45.

To overcome the problem last-mentioned and to realize certain drafting advantages about to be explained, the invention provides for a transition rule 88 which is positioned in gap 86 as shown in FIG. 4. Transition rule 88 preferably comprises a triangular shaped member or plate 90 formed of the same thickness of transparent plastic as straightedges 44 and 46. Plate 90 is provided with two supplementary straightedges 88a and 88b disposied at right angles to each other and respectively aligned parallel to the straightedge ends 44a and 46a.

Plate 90 is preferably secured to an upper reinforcing plate 92 (FIG. 3) by means of a screw knob 93. Screw knob 93 permits plate 90 to be replaced for damage or for an equivalent device and facilitates manual movement of the transition rule. Reinforcing plate 92 is in turn preferably pivotally connected to a flange 94 extending from the inner diameter side of rail 54. The connection is made by means of a pair of parallel linkage arms 96 and 98, each pivotally connected at one end 96a, 98a to flange 94 and at the other end 96b, and 98b to plate 92. Alternatively, transition rule 88 may slide along the edge of flange 94 rather than pivot as described. For this purpose an appropriate tongue and groove sliding connecting may be made 'therebetween.

Transition rule 88 is thus constructed to shift between a first operating position wherein supplementary straightedge 88a thereof abuts end 44a of primary straightedge 44 while supplementary straightedge 88b forms a continuation of primary straightedge 44 (solid lines FIG. 4), and a second operating position (dotted lines) wherein side 88b abuts end 46a of straightedge 46 while supplementary straightedge 88a forms a continuation of primary straightedge 46. Accordingly, the draftsman may use transition rule 88 to in effect extend the length of either straightedge to and through the origin into the opposite guadrant for purposes of drawing a line into or through gap 86, and matching scale indicia 89 act to extend the straightedge scales in a negative direction at the same time. It can also be seen that by shifting the transition rule from one position to the other, the draftsman may draw a complete right angle at vertex 45 without having to move drafting head 10. Further, because of the presence of transition rule 88 and since straightedges 44 and 46 have a vertex and origin coinciding with the common center line of track 30 and rail 54, a draftsman may draw intersecting radial lines at any angle in all quadrants merely by rotating but without changing the position of the drafting head. The drafting head construction also permits a complete and accurate rectangle to be drawn with only two drafting head motions as compared with the four or five motions required with conventional devices. It is important also, as is clearly shown in both FIGS. 2 and 4, that each supplementary straightedge has a zero index which, in the operating position of that straightedge, coincides with or mark the intersection point or vertex 45 of the projections of the two primary straightedges. As previously noted, this point is also the common center of rotation of the two primary straightedges as these elements are turned in unison by rotation of the support member 48. It will also be seen that the markings of the supplementary straightedges are so correlated with the truncated" markings at the adjacent ends of the primary straightedges as to provide continuous selfconsistent measurement from the previously mentioned common center of rotation of the whole straightedge assembly. Thus, there is provided a clearly defined and clearly visible origin or zero point for all measurements taken in the interval between the center point and the beginning of the primary straightedge and also for all measurements taken by reference to the continuing scale markings of the primary straightedge. Finally, in the preferred embodiments of this construction, the spacing between (1) the edge of the particular supplementary straightedge which is exposed for toolguiding use in a given operative position of the transition member 88 and (2) the near or intersectiondirected" end of the non-engaged primary straightedge is sufficient (i.e., one quarter inch or more) to provide unimpeded access: to a substantial area of the underlying drawing. This feature is illustrated by the indicated width of the gap 86 in FIG. 2, and permits drafting operations in that gap which a mere pen-admitting crevice would not accommodate. This point is further developed in connection with the description of the alternative embodiment of the invention illustrated in FIGS. 6 through 10 of the drawings.

Linkages 96 and 98 alone are sufficient to provide the necessary shifting motion of transition rule 88. However, without further means to hold rule 88 in place, the draftsman must employ one hand to keep rule 88 steady while he draws with the other. Although this situation may be acceptable, preferably an overcenter spring 100 is secured to both flange 94 and reinforcing plate 92 as by rivets 102 and 104 or the like. Spring 100 thus serves to bias and hold rule 88 in either said first or second position so that both the draftsmans hands are freed for drawing. A cover plate 106 (FIG. 2) is also preferably secured to flanGe 94 by means of screws 108 and 110 passing through cover plate support flanges 112 and 114 (FIG. 4). Cover plate 106 helps to protect linkages 96 and 98 and overcenter spring 100 from damage or blockage due to falling objects, and also serves to keep the draftsmans hands and clothing from coming into contact and possibly becoming entangled with these moving parts. An aesthetic purpose isalso served by cover plate 106 in that it covers the linkages and springs from view to produce a smooth, finished appearance to the apparatus.

A second, and in a number of respects, a preferred embodiment of the invention is illustrated in FIGS. 6 through 10 of the drawings. Referring to FIG. 6, there is shown at the left a member 126 which is assumed to be firmly connected to the main carriage 12 of FIG. 1. To this is articulated by means indicated generally at 128 and described in detail in connection with the consideration of FIG. 8, a drafting head within the scope of the present invention and described in full in the immediately following part of this specification.

The drafting head includes a carriage structure having orthogonally projecting end portions 148a and 148b which are interconnected by a bridging portion 148C extending between them. This is movably connected to and partially supported by a frame member 116 which, through an intermediate part 116a provides a journaled connection (to be described in detail at a later point) with assembly 128. This journaled connection permits the drafting head to be lifted by means of a knob 155.

As in the construction described in connection with FIG. 2, the carriage structure comprising parts 148a, b and c is movably connected to the frame member 116 by a track and roller guide combination (not shown) which permits it to be rotated in the plane of the drafting head about a center located at point 145. Also as in the case of the construction of FIG. 2, a lever, here designated as 174, functions in connection with a detent element (not shown) to lock the part 148 in selected ones of its possible rotational positions. An alternative locking means is provided by a sliding brake element 118 which, when moved in the direction of the arrow 119, frictionally engages a movable surface associated with the rotary carriage 148 in such manner as to brake its further movement. Again, in analogy with the construction of FIG. 2, the support part 148a carries a primary straightedge 144 and the support part 148b carries a similar, but orthogonally positioned primary straightedge 146. Screw knobs 150'removably attach the straightedges to the supporting members. A protractor 162 attached to the carriage '148 serves in combination with a vernier scale 158 to indicate the degree of rotation of the straightedge system as so far described.

The straightedge arrangement of FIG. 6 differs from that of FIG. 2 in that the end of the straightedge which is directed toward the center of rotation 145 is even farther displaced from that center than in the construction of FIG. 2. Specifically, the straightedge 144 terminates at the point 180, and the straightedge. 146 terminates atthe point 182. These two points are identically displaced from center point 145, andin the case illustrated, are just short of three inches removed from that point, although any displacement describable as several inches" would 's'erve. Accordingly, in the absence of the supplementarymeans now to be described, very considerable free drafting space would exist between the straightedge extremities and the boundaries imposed by the inwardly directedsurface of the annular part 154 and its associated structure. As will shortly appear, even with the supplementary means introduced, considerable free drafting space is maintained adjacent the extremity of either one straightedge or the other. This permits incidental draftingtfor example insertion ofcircles or circle centers) to be carried out in such space without need for any displacement of the primary straightedge.

In accordance with the present invention, the-advanr tage just described is accomplished without loss of the possibility of extending a line initiated alongeither the straightedge 144 or the straightedge 146 through and beyond the center point 145 by the use of interrelated supplementary straightedges now to be described. For the purpose just described, my invention provides an auxiliary rotatable member 185 having two oppositely disposed (preferably but not necessarily parallel) boundaries 185a and l85b which respectively bear calibrated straightedges, the presence of which is indicated in the drawing by markings as shown at 187. Each straightedge has a clearly identifiable zero index shown in the two cases at 189a and 189b. The member 185 underlying the two straightedges is angularly rotatable about the center point 191, which point is in fact the axial center of a bearing system, the details of which are shown in FIG. 7.

Referring to FIG. 7, the part 185 is shown as being clamped against the lower flange 195 of a bearing part 196. This bearing part is an annular cylinder which has swaged or otherwise fixed to its outer surface bearing races 198 which, in combination with outer races 200, engage ballbearings indicated at 202. The outer races are in turn secured within the part 160, previously identitied in the consideration of FIG. 6 as forming an integral part of the rotatable carriage 148. The assembly as so far described is held in place by a threaded bolt 205 screwed into cooperating threads provided in an annular nut 207 embedded in or otherwise affixed to the member 185. An enlarged head 209 provided at the upper end of the bolt 205 provides a means for readily removing it to permit replacement of the straightedgebearing member 185 if this ever becomes desirable.

With the arrangement as so far described, the member 185 is free to be moved from the horizontal operating position in which it is shown in full outline in FIG. 6 to the alternative vertical operating position in which it is shown in dotted outline. In the first case the end surface of the member 185 abuts against the terminal surface of the straightedge-bearing structure 146' engaging it closely at least at point 182, at which point it forms a continuous extension of the straightedge 146. Similarly when the part 185 is moved to its vertical position it provides a continuing extension of the straightedge 144 which it engages closely at point 180.

In the particular embodiment shown, the width of the supplementary member 185 precisely matches that of the primary straightedge bearing structures 144 and 146. This circumstance makes it readily possible to attain one of the objectives of the present invention, namely that when either of the two straightedges provided by the member 1185 is in its operating position, the zero index carried bythat straightedge will effectively coincide with the point 145 already defined as the center of rotation of the rotary carriage member 148. However, as previously described in connection with FIG. 2, the edge lines of the straightedges a and b (and correspondingly the edge lines of straightedges 144 and 146) may be displaced from projection through thecenter. point 145 by one half the thickness of the scribing point of a drafting tool, this displacement being suggested by the distance between the illustrated straightedges and the dash lines 186a and b.

It is also a desired outcome of the indicated arrangement that the extension of the. primary straightedge provided by the member 185 in each of its two operating positions passes through and beyond the center point 145, which thus becomes the vertex or origin of the orthogonal x-y system defined by the straightedges 144 and 146. This circumstance, which is clearly illustrated in FIG. 6, makes it possible to perform drafting I operations in all four quandrants about the origin 145 with minimum manipulation of the elements of the drafting head. It will be noted also that when the auxiliary member 185 is in one of its fixed positions (for example the horizontal position in which it is shown in FIG. 6), the substantial clear space earlier referred to as existing between the terminating surface of the straightedge 144 and the origin point 145 remains unobstructed and available for the insertion of' small scale details-represented by compass-drawn circles or the like. The same will be true in respect to the area to the left of the point 182 when the member 185 is thrown into its vertical position. i I

Some details concerning the structure and manipulation of the structure 185 are better shown in FIG. 9 which is a plan view of the assembly of FIG. 6 as seen from the bottom. In this Figure, parts already described in connection with FIG. 6 are identically numbered, and certain elements having to do with the guidance of the carriage 148 in its annular rotation have been removed to simplify the drawing and on the ground that they have already been fully described in connection with FIGS. 2 through 4.

In particular, FIG. 9 shows that the terminal surface 183 of straightedge 146, which surface has one of its lateral boundaries at point 182 and its other corresponding boundary at 182a, is concavely formed in the shape of an obtuse angle.

On the other hand, the abutting terminal end of the structure 185, (designated 210) follows the convex arc of a circle having its origin at the center of the bolt 205. Furthermore, as is suggested by the arrow 212, this arc is made to be tangent at 182 and 182a to the straight lines which define the obtuse angle 183. In other words, the lines defining this angle are perpendicular to the radius R of the circle drawn between the center of 205 and the points 182 and 1820. The advantage of this configuration is that while it makes possible perfect abutment of the parts 146 and 185 at the points 182 and 182a, there is no frictional engagement of the facing surfaces as part 185 is swung into its position of perative alignment with member 146. Similar cooperative arrangements are made in respect to the part 144, as indicated at point 180 in FIG. 9.

In order that the members 146 and 185 may be perfectly aligned when the member 185 is in its terminal position, there is provided a stop 220, the edge of which is of course carefully aligned with the intended locus of the back edges of the members 146 and 185. A similar stop performing a similar function in respect to the members 144 and 185, is shown at 220a.

In order to assure that the member 185 shall be firmly (but detachably) retained in the position in which it is shown in FIG. 9, this member is provided at its extremity remote from the member 146 with an attached piece of ferromagnetic material (e.g., steel ofa suitable quality) as indicated at 225. This in turn cooperates with a small permanent magnet 227 which is fixedly attached to the rotatable frame member 148. It will be understood that when the part 225 reaches a situation of close proximity to the magnet 227, there will be created a definite biasing force which will hold the part 185 in its desired position. To similarly stabilize the auxiliary member 185 when it is in its alternative position (indicated as 18%) there is provided a stop 220a and a magnet 227a which respectively corresponds to the part 220 already described.

Still referring to FIG. 9, it may be noted that to facilitate ready movement of the drafting head over the sur. face of a drafting board or drafting paper the rotatable part 148 is provided with appropriate bearing areas represented by the circles 230. These elements may for example comprise nylon buttons adhered to or otherwise secured to the lower surface of the part 148 and formed of such depth as to provide effective contact between the drafting head and the drafting paper or other underlying surface while maintaining the various straightedges in necessarily close proximity to that surface.

In order to permit all elements of the drafting head to ride up and down freely (i.e., without excessive friction) and also to facilitate ready detachment of the drafting head when this is desired, the linkage 128 between the drafting head and the other parts of the drafting mechanism may usefully be formed in the manner indicated in FIG. 8. This shows the end of a journal 128a assumed to constitute an integral part of the supporting frame 116. This journal lies in a generally conforming slot 235 formed in an enlarged and strengthened end portion 237 of the frame 126 by which connection to the driving mechanism of the drafting head is made. In order loosely to confine the journal 128a in the slot 235 there is provided an over-reaching leaf spring 242 which is adjustably positioned by means of a spring-locked screw 244. It will be understood that by manipulation of the screw 244 the journal can be released from the slot and in this way the drafting head can be separated from the remainder of the drafting machine. In addition, the configuration of the slot 235 permits the drafting head to be rotated upward from the drafting surface as required to permit access to the underlying area.

A modified application of certain aspects of the present invention is shown in FIG. 10 of the drawing. Since this figure is based largely upon the construction of FIG. 6, corresponding partsare identically numbered and not all such parts are necessarily referred to in the following description.

In FIG.'10 there is shown the angularly rotatable carriage 148 which is identical with the similarly numbered part in FIG. 6. Also, it is similarly supported in reference to the movable base structure 116. That is to say, the carriage 148 is rotatably connected to the base structure by means of an annular rail and track combination similar to that described in connection with FIGS. 2 through 4 and in connection with FIGS. 6 through 9. In this case, however, there is rotatably mounted on the pivot bolt 191 (e.g., by replacement of the part185 of FIG. 6) a member 346 having opposed (e.g., parallel) edges respectively bearing scaled straightedges 346a and 346b. Each straightedge has a clearly identifiable zero index, as respectively indicated at 348aand 348b.

The member 346 has two orthogonally related operating positions determined by alternative engagement of the member with the orthogonally directed arms 148a and 148b of the rotatable carriage 148. As described in connection with FIG. 9, these arms are provided with stop blocks 220 and 220a which serve in the present instance to limit motion of the member 346 and to assure it of desired alignment in each of its two operating positions. While not shown, magnetic anchoring means may be employed as described in connection with FIG. 9.

In the location in which the member 346 is shown in solid outline in FIG. 10, it will be seen that straightedge 346a passes to and through the center point 145 (subject only to any minor displacement that may be made to accommodate the width of a scribing tool). Also, its zero index 348a falls on the center point 148. Accordingly, with the member in the position shown, a measured line may be drawn in either direction along the straightedge 346a from the origin defined at 145. Moreover, because the distances between the pivoting point 191 and each of the straightedges 346a and 346b are equal, a similar condition will be established when the member 346 is rotated counterclockwise into the position in which it is shown in dotted outline. That is to say, in the last mentioned position, the second straightedge, 346b, will pass to and through the center point 145, and the zero index 348b will lie on that point.

It will be understood that the construction of FIG. 10 can be readily converted into the preferred and significantly more flexible construction of FIG. 6 by (1) removing the pivot bolt 191 and withdrawing the straightedge member 346, (2) replacing this member with the auxiliary part 185 of FIG. 6 and (3) attaching to the rotatable carriage parts 148a and 148b straightedges 146 and 144 respectively. Attachment may be performed by inserting retaining bolts 150 into the openings 1500 which are shown unoccupied in FIG. 10.

While my invention has been described by reference to specific embodiments thereof, it will be understood that the following claims are intended to cover all variations and equivalents which fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent is: y

l. A drafting head assembly comprising, in combination A. a base structure movable over a drafting surface, B. a rotatable carriage borne by the base structure, C. first and second primary straightedges connected with the rotatable carriage and concurrently translatable by it about its center of rotation 1. the projections of the two primary straightedges intersecting substantially at the said center of rotation regardless of the condition of rotation of the carriage about said center, and 2. the underlying structure of each straightedge terminating in an end surface spaced a substantial distance from said center, whereby'substantial space is left open between such structure and the center, and D. a supplementary rotatable member having 1. two opposed boundaries, each bearing a straightedge designed to be supplementary to one of the primary straightedges, and

2. an end surface designed to abuttingly engage the I said end surface of the underlying structure of either primary straightedge, in such fashion that one of the said supplementary straightedges provides a continuous straightline extension of the primary straightedge associated with the end surface which is engaged, E. the supplementary rotatable member being so dimensioned that its use for the purpose of extending one primary straightedge does not significantly obstruct the space left open between the said center of carriage rotation and the end surface associated with the underlying structure of the other primary straightedge, and F. the said opposed boundaries of the supplementary rotatable member being mutually parallel. 2. A drafting head assembly according to claim 1 in which each supplementary straightedge has a zero index which lies substantially at the center of rotation of the said rotatable carriage when said straightedge is in position to provide extension of one of the primary straightedges.

3. A drafting head assembly comprising, in combination A. a base structure movable over a drafting surface, B. a rotatable carriage borne by the base structure, C. first and second primary straightedges connected with the rotatable carriage and concurrently translatable by it about its center of rotation l. the projections of the two primary straightedges intersecting substantially at the said center of rotation regardless of the condition of rotation of the carriage about said center, and

2. the underlying structure of each straightedge terminating in an end surface spaced a substantial distance from said center, whereby substantial 7 space is left open between such structure and the center, and

D. a supplementary rotatable member having 1. two opposed boundaries, each bearing a straightedge designed to be supplementary to one of the primary straightedges, and

2. anend surface designed to abuttingly engage the said end surface of the underlying structure of either primary straightedge, in such fashion that one of the said supplementary straightedges provides a continuous straightline extension of the primary straightedge associated with the end surface which is engaged,

E. the supplementary rotatable member being so dimensioned that its use for the purpose of extending one primary straightedge does not significantly obstruct the space left open between the said center of carriage rotation and the end surface associated with the underlying structure of the other primary straightedge,

F. the said end surfaces of the underlying structure of the primary straightedges each being concave in the plane of the underlying structure of the associated straightedge and G. the engaging end surface of the supplementary rotatable member being convex in a degree which produces tangential contact with each of the end surfaces referred to in F of this claim 1 l at least at the outer extremities of those surfaces.

4. A drafting head assembly according to claim 3 in which the supplementary rotatable member is fixed in place by magnetic attraction when its said end surface is in operative engagement with the said end surface associated with either primary straightedge.

5. A drafting head assembly comprising in combination A. a base structure movable over a drafting surface,

B. a rotatable carriage borne by the base structure and connected with it'by an annular track providing a well-defined center of rotation for the carriage,

C. a member providing two parallel straightedges each having an identifiable zero index, said mem ber 1. being pivotally connected to the carriage for angular motion in respect to it and 2. being also capable of being moved angularly by rotational motion of the said carriage,

D. said member further having two orthogonally related operating positions in reference said carriage such that I 1. in the first said operating position, one of said straightedges passes through and beyond the center of rotation of the carriage, with its zero index point lying substantially upon said center, and

2. in the second said operating position, the other i of said straightedges passes through and beyond the center of rotation of the carriage, with its zero index lying substantially upon said center.

6. A drafting head according to claim 5 including magnetic components respectively borne by the said member and the said carriage for removably locking said member in each of its two operating positions. 

1. A drafting head assembly comprising, in combination A. a base structure movable over a drafting surface, B. a rotatable carriage borne by the base structure, C. first and second primary straightedges connected with the rotatable carriage and concurrently translatable by it about its center of rotation
 1. the projections of the two primary straightedges intersecting substantially at the said center of rotation regardless of the condition of rotation of the carriage about said center, and
 2. the underlying structure of each straightedge terminating in an end surface spaced a substantial distance from said center, whereby substantial space is left open between such structure and the center, and D. a supplementary rotatable member having
 1. two opposed boundaries, each bearing a straightedge designed to be supplementary to one of the primary straightedges, and
 2. an end surface designed to abuttingly engage the said end surface of the underlying structure of either primary straightedge, in such fashion that one of the said supplementary straightedges provides a continuous straightline extension of the primary straightedge associated with the end surface which is engaged, E. the supplementary rotatable member being so dimensioned that its use for the purpose of extending one primary straightedge does not significantly obstruct the space left open between the said center of carriage rotation and the end surface associated with the underlying structure of the other primary straightedge, and F. the said opposed boundaries of the supplementary rotatable member being mutually parallel.
 2. being also capable of being moved angularly by rotational motion of the said carriage, D. said member further having two orthogonally related operating positions in reference said carriage such that
 2. in the second said operating position, the other of said straightedges passes through and beyond the center of rotation of the carriage, with its zero index lying substantially upon said center.
 2. the underlying structure of each straightedge terminating in an end surface spaced a substantial distance from said center, whereby substantial space is left open between such structure and the center, and D. a supplementary rotatable member having
 2. an end surface designed to abuttingly engage the said end surface of the underlying structure of either primary straightedge, in such fashion that one of the said supplementary straightedges provides a continuous straightline extension of the primary straightedge associated with the end surface which is engaged, E. the supplementary rotatable member being so dimensioned that its use for the purpose of extending one primary straightedge does not significantly obstruct the space left open between the said center of carriage rotation and the end surface associated with the underlying structure of the other primary straightedge, and F. the said opposed boundaries of the supplementary rotatable member being mutually parallel.
 2. A drafting head assembly according to claim 1 in which each supplementary straightedge has a zero index which lies substantially at the center of rotation of the said rotatable carriage when said straightedge is in position to provide extension of one of the primary straightedges.
 2. the underlying structure of each straightedge terminating in an end surface spaced a substantial distance from said center, whereby substantial space is left open between such structure and the center, and D. a supplementary rotatable member having
 2. an end surface designed to abuttingly engage the said end surface of the underlying structure of either primary straightedge, in such fashion that one of the said supplementary straightedges provides a continuous straightline extension of the primary straightedge associated with the end surface which is engaged, E. the supplementary rotatable member being so dimensioned that its use for the purpose of extending one primary straightedge does not significantly obstruct the space left open between the said center of carriage rotation and the end surface associated with the underlying structure of the other primary straightedge, F. the said end surfaces of the underlying structure of the primary straightedges each being concave in the plane of the underlying structure of the associated straightedge and G. the engaging end surface of the supplementary rotatable membeR being convex in a degree which produces tangential contact with each of the end surfaces referred to in F of this claim 11 at least at the outer extremities of those surfaces.
 3. A drafting head assembly comprising, in combination A. a base structure movable over a drafting surface, B. a rotatable carriage borne by the base structure, C. first and second primary straightedges connected with the rotatable carriage and concurrently translatable by it about its center of rotation
 4. A drafting head assembly according to claim 3 in which the supplementary rotatable member is fixed in place by magnetic attraction when its said end surface is in operative engagement with the said end surface associated with either primary straightedge.
 5. A drafting head assembly comprising in combination A. a base structure movable over a drafting surface, B. a rotatable carriage borne by the base structure and connected with it by an annular track providing a well-defined center of rotation for the carriage, C. a member providing two parallel straightedges each having an identifiable zero index, said member
 6. A drafting head according to claim 5 including magnetic components respectively borne by the said member and the said carriage for removably locking said member in each of its two operating positions. 